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Yes EWI is more expensive and harder to fit
It should be vastly superior to IWI. IWI seems bonkers to me. Eats space, requires loads of disruption, almost guaranteed to cause condensation where you don't want it and mould, does nothing for the exterior.
No because the panels can (and IMO should, for as building with solid walls) be breathable.
This is correct. You aren't going to clad a single skin property with celotex for example.
Howard-
"IWI seems bonkers to me”
Depends on the property. a 6th floor flat that’s not listed but has restrictions on its exterior including windows, the options were do nothing or insulate internally.
“disruption” not when it’s done as part of a refurb in an empty flat.
“Eats space” we lost 75mm off 2 walls in bedrooms and 75mm off one wall in a 6m long lounge/diner, the gains far outweighed any loss of space.
“guaranteed to cause condensation/mould” now you are just trolling, most of the flat is cavity wall and in good condition seep vents in the cavity are there for a reason IWS or not. the one single skin wall is tile faced so not breathable.Each case/property is different, i would do it again if the property was suitable.
A shitty built victorian terrace with solid walls and a bit of slate for a damp course would be a different proposition, but then I wouldn’t ever buy one as I prefer being warm and not paying a fortune to do so.
Mr_Smyth
It's often shit, and ugly, and stops solid walls from breathing. There's no way we're keeping the current stuff we've got on the front of our place.
I've lost track of what the original scenario @apc was asking about, but they might if they have a house built before the 1930's. It's quite common to need to render over external insulation and if your house has solid brick walls you need to use something breathable.
To reinforce what you said about EWI vs IWI and the risks of condensation and damp: Yes EWI is more expensive and harder to fit, but if you don't get IWI exactly right you can easily end up with a damp or mouldy house.
With proper EWI you get higher heat flow through the wall which helps it dry out. Walls often dry towards the interior, so if you stick impervious/non-breathable insulation on the inside you end up with damper walls and any timber in those walls will also be in a damper environment.
IWI does the opposite - it lowers heat flow through the wall, reducing its ability to dry, which means you're more reliant on external finishes keeping the rain out of the walls (whereas a proper EWI system will include something that does this, then any moisture in the walls is free to move into the interior of the building, which might sound like a bad thing, but isn't). This is true even if you install a properly detailed, breathable system using hygroscopic insulation with good capillarity.